BACKGROUND: -Ventilatory efficiency (VE/VCO2 slope) is an index determined by cardiopulmonary exercise testing (CPX) which incorporates pertinent cardiac, pulmonary, and skeletal muscle physiology into a substantive composite assessment. The VE/VCO(2) slope has many applications, including utility as a well-validated prognostic gauge for heart failure (HF) patients. In this study, we combine VE/VCO(2) slope with systolic blood pressure (SBP), creating a novel index that we labeled "ventilatory power." Ventilatory power links the combined physiology inherent in the VE/VCO(2) slope to peripheral pressure, adding an additional dimension pertinent to HF assessment. Whereas the related concept of circulatory power links peak oxygen consumption (VO(2)) with peak SBP as a prognostic index, we hypothesized that ventilatory power would provide greater prognostic discrimination than VE/VO(2) slope, peak VO(2), and/or circulatory power for systolic heart failure (HF) patients. METHODS AND RESULTS: -Systolic HF patients (left ventricular ejection fraction [LVEF] ≤35%) underwent symptom-limited CPX as part of routine management and were followed for up to four years for major cardiac events (mortality, left ventricular assist device [LVAD] implantation, and heart transplantation). 875 HF patients (LVEF 26±9%; mean age 55±14) were studied. CPX indices peak VO(2), VE/VCO(2) slope, circulatory power and ventilatory power were all predictive of cardiac events (p <0.001). Multivariate analysis demonstrated that ventilatory power was the strongest indicator of prognosis. CONCLUSIONS: -While circulatory power and traditional CPX parameters can be used to predict prognosis among HF patients, ventilatory power provides relatively greater prognostic discrimination and may constitute a relatively more useful composite tool.